The present invention relates to bis(phenoxymethyl- and naphthoxymethyl)benzene derivatives which have been newly developed and their application to a heat sensitive recording paper.
In general, a heat sensitive recording paper in wide use is of the type in which a paper substrate is provided thereon with a colorant which is a colorless or pale-colored dye referred to as a leuco dye hereinafter, a phenolic compound which, as a developer, makes such a colorant assume a color when heated, a binder, a filler, an excipient, a lubricant, and other auxiliaries.
A heat sensitive recording paper produces an image in color by an instantaneous chemical reaction between a colorant and a developer when heat is applied thereto, and the applicability has been expanded from the use for copying of documents and printed matter into thermal pen type recorders in instrumentation, thermal printers, heat sensitive type automatic ticket vending machines, facsimile, etc. Especially where the application is in the information-related areas such as facsimile, demand is high for speedier operation of the apparatuses and therefore, heat sensitive recording paper used therein is required to have an ability to produce recording images of high densities speedily.
In the application of a phenolic compound as a developer, p-hydroxybenzoic acid esters, especially benzyl p-hydroxybenzoate, are known to be suitable for high speed heat sensitive recording (reference: Japanese Patent Publication Toku Kai Nos. Sho 52-140483, 56-144193, 57-82089 and 57-107885). A heat sensitive recording paper containing one of such developers lends itself to speeding up heat sensitive recording, showing a good coloring effect, producing brilliant recording images of high densities, and the plain surface being impaired much less by fog. However, the recording images developed are lacking in stability, fading and white spotting of the developed images being known as the defects. Although the reason for these defects may not always be clear, this instability is identified as crystallization of the p-hydroxybenzoic acid ester by loosening itself from the charge-transfer complex of the colorant and the p-hydroxybenzoate. It has been attempted to prevent this crystallization by addition of a certain compound but the result is not quite satisfactory.
With the above-mentioned defects taken into account the present inventors, in their research on heat sensitive recording paper, discovered new compounds which prevent the fading and the white spotting and brought the research to this invention.